function mark_offline_books() {
	var elems = $(".offline_dropitem");

	$.each(elems, function (i, elem) {
		var bookId = elem.getAttribute("data-book-id");
		var cacheId = "epube-book." + bookId;

		localforage.getItem(cacheId).then(function(book) {
			if (book) {

				elem.onclick = function() {
					offline_remove(elem, function() {
						mark_offline_books();
					});
				};

				elem.innerHTML = "Remove offline data";


			} else {
				elem.onclick = function() {
					offline_cache(bookId, function() {
						mark_offline_books();
					});
				};

				elem.innerHTML = "Make available offline";
			}
		});
	});
}

function offline_cache(bookId, callback) {
	console.log("offline cache: " + bookId);

	$.post("backend.php", {op: "getinfo", id: bookId}, function(data) {

		if (data) {
			var cacheId = 'epube-book.' + bookId;

			localforage.setItem(cacheId, data).then(function(data) {

				console.log(cacheId + ' got data');

				fetch('getbook/' + data.epub_id + ".epub", {credentials: 'same-origin'}).then(function(resp) {
					if (resp.status == 200) {
						console.log(cacheId + ' got book');

						callback();

						localforage.setItem(cacheId + '.book', resp.blob());
					}
				});

				fetch("backend.php?op=getpagination&id=" + data.epub_id, {credentials: 'same-origin'}).then(function(resp) {
					if (resp.status == 200) {
						console.log(cacheId + ' got pagination');

						resp.text().then(function(text) {
							localforage.setItem(cacheId + '.pagination', JSON.parse(text));
						});
					}
				});

				fetch("backend.php?op=getlastread&id=" + data.epub_id, {credentials: 'same-origin'}).then(function(resp) {
					if (resp.status == 200) {
						console.log(cacheId + ' got lastread');
						resp.text().then(function(text) {
							localforage.setItem(cacheId + '.lastread', JSON.parse(text));
						});
					}
				});

				if (data.has_cover) {

					fetch("backend.php?op=cover&id=" + bookId, {credentials: 'same-origin'}).then(function(resp) {

						if (resp.status == 200) {
							console.log(cacheId + ' got cover');
							localforage.setItem(cacheId + '.cover', resp.blob());
						}

					});

				}

			});
		}

	});
}